In this paper, the structural design and assembly process of continuous zoom thermal imager are studied. Vibration and shock simulation analysis are carried out at the design stage. The optical-mechanical assembly process of continuous zoom module is proposed. The measurement method of off-axis degree between narrow field and assembly reference is built. The optical axis consistency test and optical axis stabilization test are finished. The results of testing and experimental verification show that the key mechanical performance indicators are excellent, and prove that the system structure of the thermal imager is designed to meet the needs of engineering applications.